Method and apparatus for recording/reproducing optical information

ABSTRACT

A substrate ( 1 ) having a guide groove for tracking with spot irradiation light beam for recording/reproduction of information is provided with a recording layer ( 2 ) and a light transmitting layer ( 3 ). The recording layer ( 2 ) is irradiated with a spot light beam through the light transmitting layer ( 3 ) to record information on both a first portion (L′) of the recording layer corresponding to a flat section (L) between adjacent guide grooves and a second portion (G′) of the recording layer corresponding to a guide groove inside (G). Recording marks with mark lengths of nT-mT (where T is a unit length, n, m are integers of one or more, n&lt;m) are formed on the first and second portions (L′, G′). The amplitude IL 1  of a reproduced signal from the longest recording mark with the mark length of mT recorded on the first portion (L′) and the amplitude IL 2  of a reproduced signal from the longest recording mark with the mark length of mT recorded on the second portion (G′) satisfy the relation 1&lt;(IL 1 /IL 2 )&lt;1.3.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional is U.S. patent application Ser. No. 10/511,668filed Oct. 18, 2004 in the name of Suichi Ohkubo and entitled METHOD ANDAPPARATUS FOR RECORDING/REPRODUCING OPTICAL INFORMATION. Which is a U.S.National stage of application No. PCT/JP2003/004882, filed on Apr. 17,2003. Priority is claimed on that application and on the followingapplication:

Country: Japan, Application No. 2002-115448, Filed: Apr. 17, 2002

-   -   The PCT International application was published in the Japanese        language.

TECHNICAL FIELD

The present invention relates to an optical information recording mediumwith respect to which information is recorded/reproduced using lightsuch as laser light, further to an optical informationrecording/reproducing method and an optical informationrecording/reproducing apparatus using the medium, particularly to anoptical information recording medium in which information is recordedboth in a portion corresponding to the inside of a guide groove fortracking and a portion corresponding to a portion between adjacent guidegrooves with respect to a recording layer disposed on the surface of asubstrate having the guide groove for tracking, and a method andapparatus for recording/reproducing optical information using themedium.

BACKGROUND ART

As optical information recording mediums to record/reproduce informationby irradiation with laser light, a magneto-optical disk (MO), awrite-once read-many compact disk (CD-R), a rewritable compact disk(CD-RW), a write-once read-many digital video disk (DVD-R), a rewritabledigital versatile disk (DVD-RAM), a rewritable digital versatile disk(DVD-RW) and the like have been generally known. As means for raisingrecording densities in the optical information recording mediums,land/groove recording has been known in which the recording is performedin recording layer portions corresponding to both a flat portion (land)between adjacent guide grooves for tracking, the guide grooves beingformed into substantially circular shapes in parallel with one anotherin a substrate surface, and the inside (groove) of each guide groove(JP(A)-57-50330, JP(A)-9-73665, JP(A)-9-198716, JP(A)-10-64120 and thelike).

Moreover, in recent years, as a method of raising a recording density, atechnique has been proposed in which a numerical aperture (NA) of anobjective lens of an optical head constituting an apparatus forrecording/reproducing information is raised to about 0.85. When the NAis raised, a beam diameter in condensing laser light can be reduced, andtherefore it is possible to record/reproduce a finer mark. When the NAis raised in this manner, instead of applying the laser light to arecording layer through a substrate having a thickness of 0.6 to 1.2 mmas in a conventional technique, a light-transmitting layer having athickness of about 0.1 mm is formed on the recording layer of theoptical information recording medium, and the laser light can be appliedto the recording layer on the substrate via the light-transmitting layerto record and reproduce information.

It is considered that the recording density is significantly increasedby combining these techniques, that is, by performing the land/grooverecording by use of a high-NA optical head.

However, according to findings of the present inventors, in the casewhere the land/groove recording is performed using the high-NA opticalhead, there is a problem that an optical resolution differs with therecording in a recording layer portion corresponding to the flat portionbetween the guide grooves and the recording in a recording layer portioncorresponding to the inside of the guide groove. Concretely, when therecording is performed in the recording layer portion corresponding tothe flat portion between the guide grooves, a drop of a signal amplitude(on the basis of the signal amplitude of a long mark) becomes moreremarkable following a decrease of mark length, as compared with a casewhere the recording is performed in the recording layer portioncorresponding to the inside of the guide groove.

FIG. 5 is a diagram showing a relation between the mark length shown onthe abscissa and the signal amplitude shown on the ordinate. This figureshows a result of the recording performed with respect to an opticaldisk having a phase change type recording layer by the use of an opticalhead having a wavelength of 405 nm and NA=0.85. In the phase change typeoptical disk used in the present experiment, a phase difference betweenreflected lights before/after the recording is substantially 0. A linesegment denoted with reference numeral 27 shows a case where therecording is performed with respect to a portion corresponding to theinside of a guide groove, and a line segment 28 shows a case where therecording is performed with respect to one end portion of a portioncorresponding to a flat portion between the guide grooves. When thesignal amplitude in a short mark remarkably drops in the recording intothe portion corresponding to the flat portion between the guide grooves,a sufficient signal quality is not obtained, and therefore a problem hasoccurred that the high-density recording cannot be performed. An opticalresolution in a case where the recording is performed with respect tothe portion corresponding to the flat portion between the guide groovesneeds to be improved in order that the recording is performed withrespect to the portion corresponding to the inside of the guide grooveand the portion corresponding to the flat portion between the guidegrooves in such a manner as to raise the recording density.

It is to be noted that this problem is not limited to the only casewhere the information is recorded and reproduced with respect to therecording layer through the light-transmitting layer. Even in a casewhere the laser light is applied to the substrate from its back surfacein the same manner as in the conventional DVD, when the recordingdensity is raised, that is, when a shortest mark length recorded intothe disk shortens, the problem becomes remarkable. The remarkable dropof the signal amplitude in the short mark does not depend on whether therecording is performed into the portion corresponding to the flatportion between the guide grooves or the portion corresponding to theinside of the guide groove, and depends on an incidence direction of thelaser light. That is, when the recording layer is irradiated with thelaser light through the light-transmitting layer, the drop of the signalamplitude in the short mark recorded in the portion corresponding to theflat portion between the guide grooves becomes remarkable. When thelaser light is applied through the substrate, the signal amplitude dropof the short mark recorded in the portion corresponding to the inside ofthe guide groove becomes remarkable.

DISCLOSURE OF THE INVENTION

The present invention has been developed in consideration of theabove-described problems, and an object thereof is to provide an opticalinformation recording medium capable of setting recording andreproducing characteristics of a portion corresponding to a flat portionbetween guide grooves to be substantially equal to those of a portioncorresponding to the inside of the guide groove, thereby raising a trackdensity, and further enhancing a linear recording density to make itpossible to perform recording with a high density in a case where therecording is performed into both a recording layer portion correspondingto the flat portion between the guide grooves and a recording layerportion corresponding to the inside of the guide groove at a highrecording density.

In order to attain the above object, according to the present invention,there is provided an optical information recording medium in which lightis projected in a spot to thereby record/reproduce information and inwhich at least a recording layer and a light-transmitting layer aredisposed in this order on a substrate having a guide groove for trackingof the spotted light and in which the light is projected in the spot tothe recording layer from the side of the light-transmitting layer torecord the information both in a first portion of the recording layercorresponding to a flat portion between mutually adjacent guide groovesand a second portion of the recording layer corresponding to the insideof the guide groove, and the optical information recording medium hasthe following features:

(1) Recording marks with mark lengths nT to mT (where T is a unitlength, n, m are integers of one or more, n<m) are formed on both thefirst and second portions, and an amplitude IL1 of a reproduced signalfrom the longest recording mark with the mark length mT recorded on thefirst portion, and an amplitude IL2 of a reproduced signal from thelongest recording mark with the mark length mT recorded on the secondportion satisfy a relation of1<(IL1/IL2)<1.3;

(2) Recording marks with mark lengths nT to mT (where T is a unitlength, n, m are integers of one or more, n<m) are formed on both thefirst and second portions, and an amplitude IL1 of a reproduced signalfrom the longest recording mark with the mark length mT recorded on thefirst portion, an amplitude IS1 of a reproduced signal from the shortestrecording mark with the mark length nT recorded on the first portion, anamplitude IL2 of a reproduced signal from the longest recording markwith the mark length mT recorded on the second portion, and an amplitudeIS2 of a reproduced signal from the shortest recording mark with themark length nT recorded on the second portion satisfy a relation of0.7<(IS1/IL1)/(IS2/IL2)<1;

(3) Reflectance of the recording layer drops when the recording isperformed with respect to the recording layer, and a difference Δφ=φa−φcbetween a phase φa of reflected light after the recording and a phase φcof the reflected light before the recording satisfies a relation of0°<Δφ≦15°; or

(4) A reflectance of the recording layer increases when the recording isperformed with respect to the recording layer, and a difference Δφ=φa−φcbetween a phase φa of reflected light after the recording and a phase φcof the reflected light before the recording satisfies a relation of−15°≦Δφ0°.

In order to attain the above object, according to the present invention,there is also provided an optical information recording medium in whichlight is projected in a spot to thereby record/reproduce information andin which at least a recording layer is disposed on a substrate having aguide groove for tracking of the spotted light and in which the light isprojected in the spot to the recording layer from the side of thesubstrate to record the information both in a first portion of therecording layer corresponding to a flat portion between mutuallyadjacent guide grooves and a second portion of the recording layercorresponding to the inside of the guide groove, and the opticalinformation recording medium has the following features:

(5) Recording marks with mark lengths nT to mT (where T is a unitlength, n, m are integers of one or more, n<m) are formed on both thefirst and second portions, and an amplitude IL1 of a reproduced signalfrom the longest recording mark with the mark length mT recorded on thefirst portion, and an amplitude IL2 of a reproduced signal from thelongest recording mark with the mark length mT recorded on the secondportion satisfy a relation of1<(IL2/IL1)<1.3;

(6) Recording marks with mark lengths nT to mT (where T is a unitlength, n, m are integers of one or more, n<m) are formed on both thefirst and second portions, and an amplitude IL1 of a reproduced signalfrom the longest recording mark with the mark length mT recorded on thefirst portion, an amplitude IS1 of a reproduced signal from the shortestrecording mark with the mark length nT recorded on the first portion, anamplitude IL2 of a reproduced signal from the longest recording markwith the mark length mT recorded on the second portion, and an amplitudeIS2 of a reproduced signal from the shortest recording mark with themark length nT recorded on the second portion satisfy a relation of0.7<(IS2/IL2)/(IS1/IL1)<1;

(7) A reflectance of the recording layer drops when the recording isperformed with respect to the recording layer, and a difference Δφ=φa−φcbetween a phase φa of reflected light after the recording and a phase φcof the reflected light before the recording satisfies a relation of0°<Δφ≦15°; or

(8) A reflectance of the recording layer increases when the recording isperformed with respect to the recording layer, and a difference Δφ=φa−φcbetween a phase φa of reflected light after the recording and a phase φcof the reflected light before the recording satisfies a relation of−15°≦Δφ<0°.

In the above optical information recording medium, the recording layeris, for example, formed of a material whose optical reflectance or phasechanges by irradiation with laser light.

In order to attain the above object, according to the present invention,there is also provided the following methods of recording/reproducingoptical information:

A method of recording/reproducing optical information, comprising thesteps of: projecting light in spots with respect to both first andsecond portions of a recording layer of the above optical informationrecording medium (1); and forming recording marks having mark lengths nTto mT to perform recording, so that IL1 and IL2 satisfy a relation of1<(IL1/IL2)<1.3;

A method of recording/reproducing optical information, comprising thesteps of: projecting light in spots with respect to both first andsecond portions of a recording layer of the above optical informationrecording medium (2); and forming recording marks having mark lengths nTto mT to perform recording, so that IL1, IS1, IL2 and IS2 satisfy arelation of0.7<(IS1/IL1)/(IS2/IL2)<1;

A method of recording/reproducing optical information, comprising thesteps of: projecting light in spots with respect to both first andsecond portions of a recording layer of the above optical informationrecording medium (3) or (7); lowering a reflectance of the recordinglayer; and forming recording marks having mark lengths nT to mT toperform recording, so that Δφ satisfies a relation of 0°<Δφ≦15°;

A method of recording/reproducing optical information, comprising thesteps of: projecting light in spots with respect to both first andsecond portions of a recording layer of the above optical informationrecording medium (4) or (8); increasing a reflectance of the recordinglayer; and forming recording marks having mark lengths nT to mT toperform recording, so that Δφ satisfies a relation of−15°≦Δφ<0°.

A method of recording/reproducing optical information, comprising thesteps of: projecting light in spots with respect to both first andsecond portions of a recording layer of the above optical informationrecording medium (5); and forming recording marks having mark lengths nTto mT to perform recording, so that IL1 and IL2 satisfy a relation of1<(IL2/IL1)<1.3.

A method of recording/reproducing optical information, comprising thesteps of: projecting light in spots with respect to both first andsecond portions of a recording layer of the above optical informationrecording medium (6); and forming recording marks having mark lengths nTto mT to perform recording, so that IL1, IS1, IL2 and IS2 satisfy arelation of0.7<(IS2/IL2)/(IS1/IL1)<1; and

A method of recording/reproducing optical information, having a step ofprojecting light in spots using an objective lens with respect to bothfirst and second portions of a recording layer using any one of theabove optical information recording mediums (1) to (8), wherein assumingthat a wavelength of the light is λ, a numerical aperture of theobjective lens is NA, and a shortest mark length of the recording markis ML,0.25<NA·ML/λ<0.38 is established.

In order to attain the above object, according to the present invention,there is also provided an optical information recording/reproducingapparatus having an optical head which projects light in spots withrespect to both first and second portions of a recording layer using theabove optical information recording medium. The optical head has, forexample, an objective lens having a numerical aperture of 0.8 to 0.9.The optical head has, for example, a laser light source which emits thelight having a wavelength λ, and an objective lens having a numericalaperture NA, and the optical head forms the recording mark in such amanner as to establish 0.25<NA·ML/λ<0.38 assuming that a shortest marklength of the recording mark formed by irradiation with the light is ML.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially enlarged sectional view of an optical informationrecording medium according to the present invention;

FIG. 2 is a schematic diagram showing a method and apparatus forrecording/reproducing information with respect to the opticalinformation recording medium according to the present invention;

FIG. 3 is an explanatory diagram showing a relation between IL1/IL2 andan optical resolution;

FIG. 4 is an explanatory diagram showing a relation between IL1/IL2 orIL2/IL1 and a jitter of a portion corresponding to a land or a portioncorresponding to a groove; and

FIG. 5 is a diagram showing a relation between a mark length and asignal amplitude in a conventional optical information recording medium.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described hereinafter withreference to the drawings.

FIG. 1 is a partially enlarged sectional view showing one embodiment ofan optical information recording medium according to the presentinvention. Guide grooves for tracking, extended in substantiallycircular shapes around a substrate center, are formed in the surface(upper surface) of a disc-shaped support substrate 1 having a thicknessof about 1.2 mm, and a flat portion (land) L is formed between mutuallyadjacent guide grooves. The inside (bottom portion) of the guide groovefor tracking is especially shown as a groove G. A depth (groove depth)of the groove G to the land L is D. A width of the land L is typicallysubstantially equal to that of the groove G preferably within an errorof 10%. Moreover, an arrangement pitch of the groove G is, for example,0.5 to 1.2 μm.

A dielectric layer 4 is formed on the upper surface of the substrate 1,a recording layer 2 in which optical information is recorded is formedon the dielectric layer 4, a dielectric layer 5 is formed on therecording layer 2, and a light-transmitting layer 3 is formed on thedielectric layer 5. Laser light LB is applied from a light-transmittinglayer 3 side, and information is recorded/reproduced with respect to therecording layer 2. Materials such as polycarbonate (PC) and aluminum(Al) can be used for the substrate 1. The recording layer 2 has athickness of about 0.1 mm, and may be a film of PC bonded by anultraviolet cured resin or the like, or a layer formed of theultraviolet cured resin having a thickness of about 0.1 mm.

For the recording layer 2, a material whose optical reflectance or phasechanges by irradiation with the laser light, for example, a known phasechange type recording material such as GeSbTe, a known photo refractivematerial or the like can be used. The recording layer 2 has aconcave/convex shape corresponding to a land/groove shape of the surfaceof the substrate 1, and a portion (i.e., first portion) L′ correspondingto a substrate land L, and a portion (i.e., second portion) G′corresponding to a substrate groove G are formed. A depth (groove depth)of the portion G′ corresponding to the groove with respect to theportion L′ corresponding to the land in the upper surface of therecording layer 2 is d. Typically, the thickness of the recording layer2 in the portion L′ corresponding to the land is equal to that in theportion G′ corresponding to the groove. Furthermore, since thethicknesses of the dielectric layers 4, 5 in the portion correspondingto the land are similarly equal to those in the portion corresponding tothe groove, the above-described groove depth d is substantially equal toD. The thickness of the recording layer 2 is, for example, 10 to 30 nm,preferably 10 to 20 nm. In addition to functions of protective layers,the dielectric layers 4, 5 also have functions of contributing torealization of a recording medium of one of a low-to-high (L-H)recording system (the recording system in which a reflectance of therecording layer after the recording is higher than that before therecording) and a high-to-low (H-L) recording system (the recordingsystem in which the reflectance of the recording layer after therecording is lower than that before the recording), when layerconstitutions (including the thicknesses of the dielectric layers 4, 5)including these layers are appropriately set. Furthermore, thedielectric layers 4, 5 also have functions of contributing to exertionof characteristics of the present invention described later, when thethicknesses or the layer constitutions are appropriately set.

If necessary, a metal layer as a reflective film may be provided betweenthe upper surface of the substrate 1 and the dielectric layer 4.

The information is recorded/reproduced with respect to both the portionG′ corresponding to the groove and the portion L′ corresponding to theland of the recording layer 2 in the L-H recording system or the H-Lrecording system. To realize the L-H recording system or the H-Lrecording system, the respective layers, the film thicknesses, and otherlayer constitutions are appropriately set in accordance with a knowndesign method.

FIG. 2 is a schematic diagram showing embodiments of a method and anapparatus for recording/reproducing the information with respect to theabove-described optical information recording medium. An opticalinformation recording medium 10 rotates around a rotation center of avertical direction passing through the center of the medium. An opticalhead 20 constituting a recording/reproducing apparatus is disposed abovethe recording medium 10. In the optical head 20, the laser light emittedfrom a semiconductor laser 21 which is a light source is applied in aspot shape to the portion G′ corresponding to the groove or the portionL′ corresponding to the land of the recording layer 2 of the recordingmedium 10 through a collimate lens 22 and an objective lens 23. Therecording laser light is modulated in an appropriate modulation systemin accordance with recording information. The reflected light from therecording medium 10 reaches an optical detection system 25 via theobjective lens 23 and a beam splitter 24. A reproduction signal, atracking signal or the like is obtained by the optical detection system25. In the optical detection system 25, a quantity of light or a phaseof the reflected light from the recording layer 2 can be detected toobtain a required electric signal. A wavelength λ of the laser lightapplied from the semiconductor laser 21 is, for example, 390 to 680 nm,preferably 390 to 440 nm. As the objective lens 23, a lens having alarge numerical aperture (NA), for example, of 0.6 to 0.9, preferably0.8 to 0.9 is used.

It is to be noted that the present invention is not limited to theapplication of the laser light from the side of the light-transmittinglayer 3, and the laser light may be applied from the side of thesubstrate 1. In this case, a light-transmitting substrate is used as thesubstrate 1. Since the thickness of the dielectric layer 4 of theportion corresponding to the land L is typically equal to that of theportion corresponding to the groove G as described above, the depth(groove depth) of the portion L′ corresponding to the land with respectto the portion G′ corresponding to the groove is substantially D in thelower surface of the recording layer 2. When the reflective layer isformed, the layer is disposed on the recording layer 2 via thedielectric layer 5. Also in this case, the information isrecorded/reproduced with respect to both the portion G′ corresponding tothe groove and the portion L′ corresponding to the land of the recordinglayer 2 in the L-H recording system or the H-L recording system.

Therefore, when the laser light is applied from the light-transmittinglayer 3 side to record/reproduce the information into the recordinglayer 2 in the present invention, any of the following characteristics{circle around (1)} to {circle around (4)} is held.

{circle around (1)} When recording marks having mark lengths nT to mT (Tis a unit length, n, m are integers of one or more, n<m: this alsoapplies to the following) are formed using a certain modulation system,a reproduction signal amplitude IL1 of a longest mark mT recorded in theportion L′ corresponding to the land, and a reproduction signalamplitude IL2 of the longest mark mT recorded in the portion G′corresponding to the groove satisfy a relation of 1<(IL1/IL2)<1.3. Themodulation system is a system similar to a modulation system in the caseof recording/reproducing of information with respect to a conventionaloptical information recording medium, for example, a (1-7) modulationsystem, and has heretofore been known, and the present invention can beapplied to any of these known modulation systems.

{circle around (2)} When the nT to mT recording marks are formed using acertain modulation system, the reproduction signal amplitude IL1 of thelongest mark mT recorded in the portion L′ corresponding to the land, areproduction signal amplitude IS1 of a shortest mark nT recorded in theportion L′ corresponding to the land, the reproduction signal amplitudeIL2 of the longest mark mT recorded in the portion G′ corresponding tothe groove, and a reproduction signal amplitude IS2 of the shortest marknT recorded in the portion G′ corresponding to the groove satisfy arelation of 0.7<(IS1/IL1)/(IS2/IL2)<1.

{circle around (3)} When the recording is performed with respect to therecording layer 2, a reflectance of the recording layer 2 drops, and adifference Δφ=φa−φc between a phase φa of reflected light after therecording and a phase φc of the reflected light before the recordingsatisfies a relation of 0°<Δφ≦15°.

{circle around (4)} When the recording is performed with respect to therecording layer 2, the reflectance of the recording layer 2 increases,and the difference Δφ=φa−φc between the phase φa of the reflected lightafter the recording and the phase φc of the reflected light before therecording satisfies a relation of −15°≦Δφ<0°.

The present inventors have found that an optical resolution in a casewhere the recording is performed into the portion L′ corresponding tothe land using a high-NA (e.g., 0.6 to 0.9, especially 0.8 to 0.9)optical head largely changes by a ratio of the reproduction signalamplitude IL1 of the long mark recorded in the portion L′ correspondingto the land to the reproduction signal amplitude IL2 of the long markrecorded in the portion G′ corresponding to the groove. FIG. 3 is agraphic diagram showing a ratio of IL1/IL2 on the abscissa and aresolution on the ordinate, showing a relation between the ratio ofIL1/IL2 and the resolution with respect to a case (reference numeral 29)of the recording into the portion corresponding to the groove and a case(reference numeral 30) of the recording into the portion L′corresponding to the land. In FIG. 3, the resolution is defined as aratio of the reproduction signal amplitude with respect to a 0.13 μmlong mark shown in FIG. 2 and that of the reproduction signal amplitudewith respect to a 0.67 μm long mark. As shown in FIG. 3, the opticalresolution (reference numeral 30) in the case of the recording into theportion L′ corresponding to the land using the high-NA optical headlargely changes by the ratio IL1/IL2 of the reproduction signalamplitude IL1 of the longest mark recorded in the portion L′corresponding to the land to the reproduction signal amplitude IL2 ofthe longest mark recorded in the portion G′ corresponding to the groove.On the other hand, the optical resolution (reference numeral 29) in thecase of the recording performed into the portion G′ corresponding to thegroove hardly depends on the ratio IL1/IL2 of IL1 to IL2. Therefore, tomatch the optical resolution of the portion corresponding to the landwith that of the portion corresponding to the groove as much aspossible, the ratio IL1/IL2 of IL1 to IL2 may be appropriatelyregulated. That is, IL1/IL2 is set to be larger than 1 (IL1 is set to belarger than IL2) in order to match the optical resolution of the portioncorresponding to the land with that of the portion corresponding to thegroove. However, since it is difficult to increase the signal amplitudeonly of IL1 without changing the signal amplitude of IL2, IL2 needs tobe reduced in order to increase IL1/IL2. When IL2 is reduced in thismanner, a signal quality itself drops. Therefore, IL1/IL2 is set to besmaller than 1.3. Therefore, 1<(IL1/IL2)<1.3 is set.

Moreover, even in a case where a ratio of IS1/IL1 of the reproductionsignal amplitude IS1 of the shortest mark with respect to thereproduction signal amplitude IL1 of the longest mark recorded in theportion L′ corresponding to the land, and a ratio IS2/IL2 of thereproduction signal amplitude IS2 of the shortest mark with respect tothe reproduction signal amplitude IL2 of the longest mark recorded inthe portion G′ corresponding to the groove satisfy a relation of0.7<(IS1/IL1)/(IS2/IL2)<1, a difference of the resolution is remarkablyreduced between the recording into the portion G′ corresponding to thegroove and the recording into the portion L′ corresponding to the land.

Similarly, even when the difference Δφ=φa−φc between the phase φa of thereflected light after the recording and the phase φc of the reflectedlight before the recording is changed, a value of IL1/IL2 can bechanged. In the case of a material of the recording layer 2 whosereflectance drops by the recording into the recording layer 2, when thedifference Δφ=φa−φc between the phase φa of the reflected light afterthe recording and the phase φc of the reflected light before therecording satisfies a relation of 0°<Δφ≦15°, the difference of theresolution is remarkably reduced between the recording into the portionG′ corresponding to the groove and the recording into the portion L′corresponding to the land in the same manner as shown in FIG. 3.

Furthermore, in the case of a material of the recording layer 2 whosereflectance increases by the recording into the recording layer 2, whenthe difference Δφ=φa−φc between the phase φa of the reflected lightafter the recording and the phase φc of the reflected light before therecording satisfies a relation of −15°≦Δφ<0°, the difference of theresolution is remarkably reduced between the recording into the portionG′ corresponding to the groove and the recording into the portion L′corresponding to the land in the same manner as shown in FIG. 3.

Therefore, when laser light LB is applied to the recording layer 2 fromthe light-transmitting layer 3 side to record/reproduce the information,and when any of the above-described conditions {circle around (1)} to{circle around (4)} is satisfied, the difference of the resolution isremarkably reduced between the recording into the portion G′corresponding to the groove and the recording into the portion L′corresponding to the land.

On the other hand, in a case where the laser light is applied from theback surface (lower surface) of the substrate 1 unlike FIG. 1, contraryto FIG. 5, since the drop of the reproduction signal amplitude of theshort mark is remarkable in the portion G′ corresponding to the groove,the present invention has any of the following characteristics {circlearound (5)} to {circle around (8)}.

{circle around (5)} When the nT to mT recording marks are formed using acertain modulation system, the reproduction signal amplitude IL1 of thelongest mark mT recorded in the portion L′ corresponding to the land,and the reproduction signal amplitude IL2 of the longest mark mTrecorded in the portion G′ corresponding to the groove satisfy arelation of 1<(IL2/IL1)<1.3.

{circle around (6)} When the nT to mT recording marks are formed using acertain modulation system, the reproduction signal amplitude IL1 of thelongest mark mT recorded in the portion L′ corresponding to the land,the reproduction signal amplitude IS1 of the shortest mark nT recordedin the portion L′ corresponding to the land, the reproduction signalamplitude IL2 of the longest mark mT recorded in the portion G′corresponding to the groove and the reproduction signal amplitude IS2 ofthe shortest mark nT recorded in the portion G′ corresponding to thegroove satisfy a relation of 0.7<(IS2/IL2)/(IS1/IL1)<1.

{circle around (7)} When the recording is performed with respect to therecording layer 2, the reflectance of the recording layer 2 drops, andthe difference Δφ=φa−φc between the phase φa of reflected light afterthe recording and the phase φc of the reflected light before therecording satisfies a relation of 0°<Δφ≦15°.

{circle around (8)} When the recording is performed with respect to therecording layer 2, the reflectance of the recording layer 2 increases,and the difference Δφ=φa−φc between the phase φa of the reflected lightafter the recording and the phase φof the reflected light before therecording satisfies a relation of −15°≦Δφ<0°.

A phenomenon in which the resolution rapidly changes depending on thevalue of IL1/IL2 in the portion L′ corresponding to the land in a casewhere the laser light is applied to the recording layer 2 from thelight-transmitting layer 3 side or in the portion G′ corresponding tothe groove in a case where the laser light is applied to the recordinglayer 2 from the substrate 1 side is a phenomenon determined only by theoptical phase difference between the reflected lights before/after therecording. That is, even in an optical disk different in a compositionor thickness of the recording layer 2, a type or thickness of thedielectric layer or the like, a satisfactory resolution can be realized,when IL1/IL2 is designed into a desired value.

Effects of the present invention will be further described in accordancewith examples of the present invention together with comparativeexamples out of the scope of the present invention.

EXAMPLE 1

A disc-shaped PC substrate having a thickness of 1.1 mm was used as asubstrate, and a 100 nm thick Al reflective film, a 15 nm thick ZnS-SiO₂dielectric layer, a 15 nm thick GeSbTe recording layer, and a 40 to 85nm thick ZnS—SiO₂ dielectric layer were stacked/formed on a land/grooveformed surface of the substrate by sputtering. On the layers, a 0.1 mmthick PC film was bonded as a light-transmitting layer by an ultravioletcured resin.

After initializing (crystallizing) the above-described disk (recordingmedium), the disk was rotated at a linear speed of 5.1 m/s, laser lightwas applied from a light-transmitting layer side using an optical headhaving a wavelength of 405 nm, NA=0.85, recording was performed intoboth a portion L′ corresponding to a land and a portion G′ correspondingto a groove on a linear density condition of 0.116 μm/bit, andreproduction characteristics were measured. Since (1-7) modulation wasused as a modulation system, a mark length of a longest mark was 8T, anda mark length of a shortest mark was 2T. IL1 and IL2 correspond to anamplitude of an 8T reproduction signal, and IS1 and IS2 correspond to anamplitude of a 2T reproduction signal.

Table 1 shows a relation between optical characteristics andrecording/reproducing characteristics at a time when the thickness ofthe ZnS—SiO₂ dielectric layer on the recording layer is changed. Sincethe recording layer is in a crystallized state before the recording, andbrought into an amorphous state after the recording, φa corresponds to aphase of reflected light at a time when the recording layer is in theamorphous state, and φc corresponds to a phase of the reflected light ata time when the recording layer is in the crystallized state.

It is to be noted that a recording power was set to such a power that asecondary higher harmonic wave distortion of an 8T reproduction signalwas minimized in each of the portion L′ corresponding to the land andthe portion G′ corresponding to the groove, but as shown in Table 1, therecording power of the portion L′ corresponding to the land wassubstantially equal to that of the portion G′ corresponding to thegroove, and a difference between them was 5% less. TABLE 1 ZnS—SiO₂Reflectance Refl. Rec. film before after Jitter power thicknessrecording rec. φ_(a) − φ_(c) IL1/ (IS1/IL1)/ (%) (mW) (nm) (%) (%)(deg.) IL2 (IS2/IL2) L′ G′ L′ G′ 40 18 1 −5 0.93 0.55 8.7 18 4.5 4.3 5019 1.5 0 1 0.65 9 15 4.6 4.5 60 20 2 4 1.08 0.8 9.5 11 4.8 4.7 70 17 0.510 1.2 0.92 9.8 10.5 4.6 4.6 80 15 0.3 15 1.28 0.98 10 9.5 4.3 4.2 85 140.2 20 1.34 1.03 13 9.2 4.2 4

In the case of the recording layer whose reflectance drops by therecording, it has been found that substantially equal jittercharacteristics are obtained in the portion L′ corresponding to the landand the portion G′ corresponding to the groove, when one of conditions0°<Δφ≦15°, 1<IL1/IL2<1.3, and 0.7<(IS1/IL1)/(IS2/IL2)<1.0 is satisfied.Especially, in 1.1<IL1/IL2<1.3, there is little difference of the jittercharacteristics between the portion L′ corresponding to the land and theportion G′ corresponding to the groove, and the jitters are balanced.

EXAMPLE 2

A disc-shaped PC substrate having a thickness of 1.1 mm was used as asubstrate, and a 100 nm thick Al reflective film, a 25 nm thick ZnS—SiO₂dielectric layer, a 15 nm thick GeSbTe recording layer, a 25 nm thickZnS—SiO₂ dielectric layer, a 30 nm thick SiO₂ dielectric layer, and a 50to 75 nm thick ZnS—SiO₂ dielectric layer were successivelystacked/formed on a land/groove formed surface of the substrate bysputtering. On the layers, a 0.1 mm thick PC film was bonded as alight-transmitting layer by an ultraviolet cured resin.

After initializing (crystallizing) the above-described disk, the diskwas rotated at a linear speed of 5.1 m/s, laser light was applied from alight-transmitting layer side using an optical head having a wavelengthof 405 nm, NA=0.85, recording was performed into both a portion L′corresponding to a land and a portion G′ corresponding to a groove on alinear density condition of 0.116 μm/bit, and reproductioncharacteristics were measured. Since (1-7) modulation was used as amodulation system, a mark length of a longest mark was 8T, and a marklength of a shortest mark was 2T. IL1 and IL2 correspond to an amplitudeof an 8T reproduction signal, and IS1 and IS2 correspond to an amplitudeof a 2T reproduction signal.

Table 2 shows a relation between optical characteristics andrecording/reproducing characteristics at a time when the thickness ofthe ZnS—SiO₂ dielectric layer of an uppermost layer is changed. Sincethe recording layer is in a crystallized state before the recording, andbrought into an amorphous state after the recording, φa corresponds to aphase of reflected light at a time when the recording layer is in theamorphous state, and φc corresponds to a phase of the reflected light ata time when the recording layer is in the crystallized state.

It is to be noted that in the present example, a recording power was setto such a power that symmetry of an eye pattern in recording a randomsignal was optimized in each of the portion L′ corresponding to the landand the portion G′ corresponding to the groove, but as shown in Table 2,the recording power of the portion L′ corresponding to the land wassubstantially equal to that of the portion G′ corresponding to thegroove, and a difference between them was 5% less. TABLE 2 ZnS—SiO₂Reflectance Refl. Rec. film before after Jitter power thicknessrecording rec. φ_(a) − φ_(c) IL1/ (IS1/IL1)/ (%) (mW) (nm) (%) (%)(deg.) IL2 (IS2/IL2) L′ G′ L′ G′ 50 5.8 20 4 0.95 0.55 8.4 17 4.2 4.0 556 21 0 1 0.68 8.8 14.5 4.3 4.1 60 6.2 22 −3 1.04 0.75 9.1 10.5 4.3 4.265 6.5 23 −8 1.13 0.9 9.5 9.5 4.3 4.2 70 7 24 −14 1.27 0.97 9.8 8.8 4.44.2 75 8 26 −18 1.32 1.02 13 8.5 4.5 4.3

In a case where the reflectance of the recording layer increases by therecording, it has been found that substantially equal jittercharacteristics are obtained in the portion L′ corresponding to the landand the portion G′ corresponding to the groove, when one of conditions−15°≦Δφ≦0°, 1 IL1/IL2<1.3, and 0.7<(IS1/IL1)/(IS2/IL2)<1.0 is satisfied.Especially, in 1.1<IL1/IL2<1.3, there is little difference of the jittercharacteristics between the portion L′ corresponding to the land and theportion G′ corresponding to the groove, and the jitters are balanced.

EXAMPLE 3

A disc-shaped PC substrate having a thickness of 0.6 mm was used as asubstrate, and a 40 to 85 nm thick ZnS—SiO₂ dielectric layer, a 15 nmthick GeSbTe recording layer, a 15 nm thick ZnS—SiO₂ dielectric layer,and a 100 nm thick Al reflective film were successively stacked/formedon a land/groove formed surface of the substrate by sputtering. On thelayers, a 0.6 mm thick glass substrate was bonded by an ultravioletcured resin.

After initializing (crystallizing) the above-described disk (recordingmedium), the disk was rotated at a linear speed of 3.5 m/s, laser lightwas applied from the back surface of the PC substrate using an opticalhead having a wavelength of 405 nm, NA=0.65, recording was performedinto both a portion L′ corresponding to a land and a portion G′corresponding to a groove on a linear density condition of 0.16 μm/bit,and reproduction characteristics were measured. Since (1-7) modulationwas used as a modulation system, a mark length of a longest mark was 8T,and a mark length of a shortest mark was 2T. IL1 and IL2 correspond toan amplitude of an 8T reproduction signal, and IS1 and IS2 correspond toan amplitude of a 2T reproduction signal.

Table 3 shows a relation between optical characteristics andrecording/reproducing characteristics at a time when the thickness ofthe ZnS—SiO₂ dielectric layer on the PC substrate is changed. Since therecording layer is in a crystallized state before the recording, andbrought into an amorphous state after the recording, φa corresponds to aphase of reflected light at a time when the recording layer is in theamorphous state, and φc corresponds to a phase of the reflected light ata time when the recording layer is in the crystallized state.

It is to be noted that in the present example, a recording power was setto such a power that a secondary higher harmonic wave distortion of the8T reproduction signal was minimized in each of the portion L′corresponding to the land and the portion G′ corresponding to thegroove, but as shown in Table 3, the recording power of the portion L′corresponding to the land was substantially equal to that of portion G′corresponding to the groove, and a difference between them was 5% orless. TABLE 3 ZnS—SiO₂ Reflectance Refl. Rec. film before after Jitterpower thickness recording rec. φ_(a) − φ_(c) IL2/ (IS2/IL2)/ (%) (mW)(nm) (%) (%) (deg.) IL1 (IS1/IL1) L′ G′ L′ G′ 40 18 1 −5 0.93 0.55 8.517 5.8 5.6 50 19 1.5 0 1 0.68 8.8 14.5 5.8 5.6 60 20 2 4 1.08 0.75 9.310.6 6 5.8 70 17 0.5 10 1.2 0.9 9.6 10.2 5.8 5.6 80 15 0.3 15 1.28 0.979.9 10 5.6 5.4 85 14 0.2 20 1.34 1.02 12.9 9.3 5.5 5.3

In a case where the reflectance of the recording layer drops by therecording, it has been found that substantially equal jittercharacteristics are obtained in the portion L′ corresponding to the landand the portion G′ corresponding to the groove, when one of conditions0°<Δφ≦15°, 1<IL2/IL1<1.3, and 0.7<(IS2/IL2)/(IS1/IL1)<1.0 is satisfied.Especially, in 1.1<IL2/IL1<1.3, there is little difference equal jittercharacteristics between the portion L′ corresponding to the land and theportion G′ corresponding to the groove, and the jitters are balanced.

EXAMPLE 4

A disc-shaped PC substrate having a thickness of 0.6 mm was used as asubstrate, and a 50 to 75 nm thick ZnS—SiO₂ dielectric layer, a 30 nmthick SiO₂ dielectric layer, a 25 nm thick ZnS—SiO₂ dielectric layer, a15 nm thick GeSbTe recording layer, a 25 nm thick ZnS—SiO₂ dielectriclayer, and a 100 nm thick Al reflective film were successivelystacked/formed on a land/groove formed surface of the substrate bysputtering. On the layers, a 0.6 mm thick glass substrate was bonded byan ultraviolet cured resin.

After initializing (crystallizing) the above-described disk, the diskwas rotated at a linear speed of 3.5 m/s, laser light was applied fromthe back surface of the PC substrate using an optical head having awavelength of 405 nm, NA=0.65, recording was performed into both aportion L′ corresponding to a land and a portion G′ corresponding to agroove on a linear density condition of 0.16 μm/bit, and reproductioncharacteristics were measured. Since (1-7) modulation was used as amodulation system, a mark length of a longest mark was 8T, and a marklength of a shortest mark was 2T. IL1 and IL2 correspond to an amplitudeof an 8T reproduction signal, and IS1 and IS2 correspond to an amplitudeof a 2T reproduction signal.

Table 4 shows a relation between optical characteristics andrecording/reproducing characteristics at a time when the thickness ofthe ZnS—SiO₂ dielectric layer just on the substrate is changed. Sincethe recording layer is in a crystallized state before the recording, andbrought into an amorphous state after the recording, φa corresponds to aphase of reflected light at a time when the recording layer is in theamorphous state, and φc corresponds to a phase of the reflected light ata time when the recording layer is in the crystallized state.

It is to be noted that in the present example, a recording power was setto such a power that symmetry of an eye pattern in recording a randomsignal was optimized in each of the portion L′ corresponding to the landand the portion G′ corresponding to the groove, but as shown in Table 4,the recording power of the portion L′ corresponding to the land wassubstantially equal to that of the portion G′ corresponding to thegroove, and a difference between them was 5% less. TABLE 4 ZnS—SiO₂Reflectance Refl. Rec. film before after Jitter power thicknessrecording rec. φ_(a) − φ_(c) IL2/ (IS2/IL2)/ (%) (mW) (nm) (%) (%)(deg.) IL1 (IS1/IL1) L′ G′ L′ G′ 50 5.8 20 4 0.95 0.55 8.2 16.5 5.5 5.455 6 21 0 1 0.68 8.6 14.4 5.5 5.3 60 6.2 22 −3 1.04 0.75 9 10.2 5.6 5.465 6.5 23 −8 1.13 0.9 9.4 9.3 5.6 5.6 70 7 24 −14 1.27 0.97 9.7 8.7 5.85.6 75 8 26 −18 1.32 1.02 12.8 8.4 6 5.8

In a case where the reflectance of the recording layer increases by therecording, it has been found that substantially equal jittercharacteristics are obtained in the portion L′ corresponding to the landand the portion G′ corresponding to the groove, when one of conditions−15°≦Δφ<0°, 1<IL2/IL1<1.3, and 0.7<(IS2/IL2)/(IS1/IL1)<1.0 is satisfied.Especially, in 1.1<IL2/IL1<1.3, there is little difference of the jittercharacteristics between the portion L′ corresponding to the land and theportion G′ corresponding to the groove, and the jitters are balanced.

FIG. 4 shows the results of Tables 1 to 4 together. In FIG. 4, theabscissa shows IL1/IL2 in a case where the laser light is applied to therecording layer from the light-transmitting layer side (corresponding toExamples 1 and 2), and IL2/IL1 in a case where the laser light isapplied to the recording layer from the PC substrate side (correspondingto Examples 3 and 4), respectively. The ordinate of FIG. 4 shows anabsolute value A6 of the difference of the jitter between the portion L′corresponding to the land and the portion G′ corresponding to thegroove. As seen from FIG. 4, the jitters of the portion L′ correspondingto the land and the portion G′ corresponding to the groove are balancedvery well irrespective of the decrease or increase of the reflectance ofthe recording layer by the recording in the case of 1<IL1/IL2<1.3,especially 1.1<IL1/IL2<⅓, when the laser light is applied to therecording layer from the light-transmitting layer side, or in the caseof 1<IL2/IL1<1.3, especially 1.1<IL2/IL1<1.3, when the laser light isapplied to the recording layer from a PC substrate side.

As seen from FIG. 5, even by the use of an optical disk having a phasedifference of substantial 0, when the linear recording density is low,the resolution of the portion corresponding to the land is substantiallyequal to that of the portion corresponding to the groove, and thereforea large effect cannot be obtained even by the use of the presentinvention in a case where the recording/reproducing is performed at alow density. With respect to the optical disk whose phase difference issubstantially 0, a length of a recording mark in which the resolutiondiffers by 3 dB or more in the portions corresponding to the land andgroove is 0.18 μm or less, as seen from FIG. 5, in a case where anoptical head, for example, having λ=405 nm, NA=0.85 is used. Consideringthat a beam diameter of the optical head is proportional to λ/NA, andassuming that the length of the shortest mark formed on the optical diskis ML, a ratio a=NA·ML/λ of ML to λ/NA is an index of the recordingdensity. When FIG. 5 is reviewed with this index, a=0.38 or less at therecording density at which the resolution differs by 3 dB or more. Whena is 0.25 or less, there is exceeded an optical diffraction limit, andthe signal itself is not obtained. Therefore, the recording density atwhich an effect of enhancing the characteristics is obtained by the useof the optical information recording medium according to the presentinvention corresponds to a range of 0.25<a <0.38. It is to be noted thatalthough not shown in FIG. 5, the resolution differs by 3 dB or more ina case where a is 0.38 or less even by the use of the optical headhaving NA=0.65. The conditions on which the resolution differs by 3 dBare the same as conditions on which a ratio of IS1/IL1 to IS2/IL2 is0.7, and correspond to conditions on which satisfactory characteristicsare obtained in the portions corresponding to the land and the groove asdescribed in the present description.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, recording can beperformed with respect to both a portion corresponding to a land and aportion corresponding to a groove of a recording layer at a highrecording density, and it is therefore possible to obtain alarge-capacity optical information recording medium.

1. An optical information recording medium in which light is projectedin a spot to thereby record/reproduce information and in which at leasta recording layer and a light-transmitting layer are disposed in thisorder on a substrate having a guide groove for tracking of the spottedlight and in which the light is projected in the spot to the recordinglayer from the side of the light-transmitting layer to record theinformation both in a first portion of the recording layer correspondingto a flat portion between mutually adjacent guide grooves and a secondportion of the recording layer corresponding to the inside of the guidegroove, wherein a reflectance of the recording layer drops when therecording is performed with respect to the recording layer, and adifference Δφ=φa−φc between a phase φa of reflected light after therecording and a phase φc of the reflected light before the recordingsatisfies a relation of 0°<Δφ≦15°.
 2. An optical information recordingmedium in which light is projected in a spot to thereby record/reproduceinformation and in which at least a recording layer and alight-transmitting layer are disposed in this order on a substratehaving a guide groove for tracking of the spotted light and in which thelight is projected in the spot to the recording layer from the side ofthe light-transmitting layer to record the information both in a firstportion of the recording layer corresponding to a flat portion betweenmutually adjacent guide grooves and a second portion of the recordinglayer corresponding to the inside of the guide groove, wherein areflectance of the recording layer increases when the recording isperformed with respect to the recording layer, and a difference Δφ=φa−φcbetween a phase φa of reflected light after the recording and a phase φcof the reflected light before the recording satisfies a relation of−15°≦Δφ<0°.
 3. An optical information recording medium in which light isprojected in a spot to thereby record/reproduce information and in whichat least a recording layer is disposed on a substrate having a guidegroove for tracking of the spotted light and in which the light isprojected in the spot to the recording layer from the side of thesubstrate to record the information both in a first portion of therecording layer corresponding to a flat portion between mutuallyadjacent guide grooves and a second portion of the recording layercorresponding to the inside of the guide groove, wherein a reflectanceof the recording layer drops when the recording is performed withrespect to the recording layer, and a difference Δφ=φa−φc between aphase φa of reflected light after the recording and a phase φc of thereflected light before the recording satisfies a relation of 0°<Δφ≦15°.4. An optical information recording medium in which light is projectedin a spot to thereby record/reproduce information and in which at leasta recording layer is disposed on a substrate having a guide groove fortracking of the spotted light and in which the light is projected in thespot to the recording layer from the side of the substrate to record theinformation both in a first portion of the recording layer correspondingto a flat portion between mutually adjacent guide grooves and a secondportion of the recording layer corresponding to the inside of the guidegroove, wherein a reflectance of the recording layer increases when therecording is performed with respect to the recording layer, and adifference Δφ=φa−φc between a phase φa of reflected light after therecording and a phase φc of the reflected light before the recordingsatisfies a relation of −15°≦Δφ<0°.
 5. A method of recording/reproducingoptical information, comprising the steps of: projecting light in spotswith respect to both first and second portions of a recording layer ofthe optical information recording medium according to claim 1; loweringa reflectance of the recording layer; and forming recording marks havingmark lengths nT to mT to perform recording, so that Δφ satisfies arelation of 0°<Δφ≦15°.
 6. A method of recording/reproducing opticalinformation, comprising the steps of: projecting light in spots withrespect to both first and second portions of a recording layer of theoptical information recording medium according to claim 2; increasing areflectance of the recording layer; and forming recording marks havingmark lengths nT to mT to perform recording, so that Δφ satisfies arelation of −15≦Δφ<0°.